Natural Crop Protection in the Tropics: Promoting natural enemies

Promoting natural enemies

One of the most important components of integrated pest management is the management of natural enemies. These include the parasitoids, arthropod predators and pathogens, but also the larger predators such as frogs, toads, birds, lizards, and snakes. Promoting natural enemies is not only for the specialist entomologists and companies which sell pathogens and beneficial insects, but is the prime task of the farmer. Promoting natural enemies means managing the farm to create a friendly environment for these pest management 'farm workers'. Awareness of their benefits and needs enables farmers to create the optimal environment so that they can do a good job. The optimal environment means firstly a diversified farming system that creates suitable habitats for the natural enemies, so that they are on site when needed. Intercropping and mixed cropping as described in the "Intercropping" section above contribute to this. Secondly it means managing these assistants, delegating the work to them by giving them signals showing where exactly their action is required. Thirdly it means farmers actively protecting, promoting and propagating them. Some of the signals and methods that are based on practical experience are presented below.

Ants have been found to be good predators of a number of insect pests, particularly the carnivorous species such as weaver ants, soldier ants, and others. As they are social insects and do not move widely they are reasonably easy to manage. Ants are the most important group of predators in Africa, comparable to the spiders in Southeast Asia. The following sections give some practical ideas for managing and promoting ants.

Attracting ants with sugar-water

This technique is based on the idea of applying 'artificial honeydews' to crops to concentrate natural enemies in the field. Such honeydews can be made from sugar, jaggery, molasses etc., and consist of sucrose and/or proteins, which are nutrients to natural enemies. Applying them to crops has been shown to attract ants, but also ladybird beetles, lacewings, hover flies, big-eyed bugs, and minute pirate bugs. This technique could be a very attractive alternative to pesticides for small farmers in the tropics, thanks to low/no risk of poisoning in application, the ease of preparation and application, and the ready availability of sucrose sources.

An example is the application of sugar solution for the control of the fall armyworm, Spodoptera frugiperda. This was developed as a joint effort between farmers and scientists. In a training course on natural pest control in Honduras, farmers learned about the benefits of natural enemies and their biology. In this course, Sra. Maria Castro learned that ants were predators of insect pests. Having previously observed that ants like sweet things, she began using a sugar-water solution to attract ants to her maize field for control of fall armyworm. Subsequently, an experiment was set up to observe the activity of natural enemies in maize treated with sugar solutions. A sugar solution was prepared using 90 g sugar per litre water. For one hectare, about 17 kg of sugar are needed. The applications began one week after plant emergence, and were conducted at weekly intervals for five weeks until the maize reached a height of 1.5m.

The following observations and recommendations resulted from this study:

• On average, twice the numbers of predators were found in maize treated with sugar than in the non-treated maize.

• The most abundant predator recorded was the fire ant, Solenopsis geminata. Other predators were ladybird beetles, spiders, lacewings, assassin bugs, and social wasps.

• Leaf area damage was 35% less in sugar-treated maize than in non-treated maize, whereas whorl infestation was 18% less in maize treated with sugar. This lead to the conclusion that fire ants predate the smaller larvae more than the larger larvae that cause the whorl damage.

The printed version contains more information about:

Weaver ants in orchards and groves

Soldier ants

Beetle larvae control

Attracting birds with turmeric-rice